1. Field of the Invention
The present invention relates to a solid-state image pickup element for outputting a signal of incident video light and an image pickup apparatus using the same.
2. Related Background Art
A solid-state image pickup element according to a first example of prior art will be described.
FIG. 1 is a circuit diagram of the solid-state image pickup element of the first example of prior art. Referring to FIG. 1, the solid-state image pickup element comprises a photodiode 101 as a photodetecting element for generating charges corresponding to incident light, a floating diffusion region 102, a transfer transistor 103 for transferring charges generated by the photodiode 101 to the floating diffusion region 102, a reset transistor 104 for removing charges stored in the floating diffusion region 102, amplification transistors 105, 106, and 107, a capacitor 108 for storing a voltage generated in the floating diffusion region upon resetting, a capacitor 109 for storing a voltage generated in the floating diffusion region in an operative state, a switching transistor 110 for connecting an amplifier to the capacitor 108, a switching transistor 111 for connecting an amplifier to the capacitor 109, a capacitor discharging transistor 112 for discharging the capacitors 108 and 109, buffers 113 and 114, switching transistors 115 and 116 for switching the capacitors 108 and 109 to capacitors of another line and supplying the voltages of the capacitors 108 and 109 to the buffers 113 and 114, respectively, reset transistors 117 and 118 for resetting input voltages to the buffers 113 and 114, respectively, horizontal output lines 119 and 120, a vertical scanning circuit 121, and a horizontal scanning circuit 122. The amplifier formed from the transistors 105, 106, and 107 serves as a source-follower-type amplifier only when the transistors 106 and 107 are ON. The photodiode 101, floating diffusion region 102, and transistors 103, 104, 105, and 106 form one pixel.
FIG. 2 is a timing chart showing the operation timing of the solid-state image pickup element shown in FIG. 1. The operation of the solid-state image pickup element shown in FIG. 1 will be described with reference to FIGS. 1 and 2.
At time T801, a vertical scanning start pulse is input to a terminal 2,: a vertical scanning pulse is input to a terminal 3 to select the first line, and a signal 20a goes high (not shown). A pulse of high level is input to a terminal 8 to reset the floating diffusion region 102. Terminals 11, 12, and 13 are simultaneously set at high level, and the capacitors 108 and 109 are reset. At time T802, the reset pulse at the terminal 8 goes low to set the floating diffusion region 102 in an electrically floating state. At time T803, a pulse of high level is applied to a terminal 10, and simultaneously, a pulse of high level is applied to the terminal 12, so the voltage (reset voltage) immediately after resetting the floating diffusion region 102 is read out to the capacitor 108. At time T804, a pulse of high level is applied to a terminal 9 to transfer charges generated by the photodiode 101 to the floating diffusion region 102. At time T805, pulses of high level are applied to the terminals 10 and 13 to read out the voltage (signal voltage+reset voltage) of the floating diffusion region 102 to the capacitor 109. At time T806, the voltage at a terminal 14 changes from high level to low level to reset the horizontal output lines 119 and 120. At the same time, a horizontal scanning start pulse is input to a terminal 5, and a horizontal scanning pulse is input to a terminal 6 to start the signal read from line memories formed from capacitors of the respective columns. The input signal to the terminal 14 is in an opposite phase to that of the horizontal scanning pulse to prevent interference between the capacitors of the respective columns. Reset voltages of the respective columns are sequentially output from a terminal 16. Sums of signal voltages and reset voltages of the respective columns are sequentially output from a terminal 17. When the difference between two outputs is calculated by a subtracting means connected to the output side, a signal voltage containing no reset voltage that varies between pixels can be obtained. Hence, an output with a high S/N ratio, which contains no noise component due to a variation in reset voltage, can be obtained.
The photodiode 101 is reset at time T804 when charges are transferred from the photodiode 101 to the floating diffusion region 102. Resetting is completed when the signal at the terminal 9 goes low to end transfer. After this, storage of charges corresponding to incident light is restarted. This storage operation continues until T804 of the next frame cycle.
From time T801B, the signals input to the terminals 3, 8, 9, 10, 11, 12, 13, 5, 6, and 14 repeat their patterns from time T801 to time T801B. Referring to FIG. 3, by operation of the vertical scanning circuit 121, the signal 20a goes high during only the first line period. Sequentially, a signal 20b goes high during only the second line period, and then, a signal 20c goes high during only the third line period. Because of the presence of a gate group 123, signals supplied to the terminals 8, 9, and 10 become valid for only the first line during the first line period, for only the second line during the second line period, and for only the third line during the third line period, and this also applies to the following lines.
Hence, signals output from the terminals 16 and 17 are signals stored in the photodiodes at timings that sequentially shift in units of lines. This scheme is called a rolling shutter scheme.
The floating diffusion region 102 holds the transferred charges after charge transfer from the photodiode 101 until resetting and therefore functions as a memory.
A second example of prior art will be described next.
FIG. 4 is a circuit diagram of a solid-state image pickup element of the second example of prior art. The same reference numerals as in the first example of prior art shown in FIG. 1 denote the same parts in FIG. 4, and a detailed description thereof will be omitted. A gate group 123 has the same arrangement as in the first example of prior art although it is represented by different symbols. In the second example of prior art, an OR gate 124 is inserted between the output terminal of the elements of the gate group 123 for receiving a signal from a terminal 9 and the gate of a transfer transistor 103.
FIG. 5 is a timing chart showing the operation timings of the solid-state image pickup element shown in FIG. 4. The operation of the solid-state image pickup element shown in FIG. 4 will be described with reference to FIGS. 4 and 5.
At time T901, pulses of high level are applied to terminals 8 and 19 to reset floating diffusion regions 102 of all pixels and reset photodiodes 101 of all pixels. When resetting is ended, storage of charges corresponding to incident light by the photodiodes 101 of all pixels is started. At time T902, a pulse of high level is applied to the terminal 19 again to transfer charges stored in the photodiodes 101 of all pixels to the floating diffusion regions 102. After this pulse of high level goes low, the charges transferred to the floating diffusion regions 102 are held. At time T903, a vertical scanning start pulse is input to a terminal 2, and a vertical scanning pulse is input to a terminal 3 to select the first line, and a signal 20a goes high (not shown). At time T903, pulses of high level are applied to terminals 11, 12, and 13 to reset capacitors 108 and 109. At time T904, pulses of high level are applied to terminals 10 and 12 to read out (signal voltage+reset voltage) from the photodiode of the floating diffusion region 102 to a capacitor 110. At time T905, a pulse of high level is applied to the terminal 8 to reset the floating diffusion region 102. At time T906, pulses of high level are applied to the terminals 10 and 13 to read out the reset voltage of the floating diffusion region 102 to the capacitor 109. At time T906, the voltage at a terminal 14 changes from high level to low level to reset horizontal output lines 119 and 120. At time same time, a horizontal scanning start pulse is input to a terminal 5, and a horizontal scanning pulse is input to a terminal 6 to start the signal read from line memories formed from capacitors of the respective columns. The input signal to the terminal 14 is in an opposite phase to that of the horizontal scanning pulse to prevent interference between the capacitors of the respective columns. Reset voltages of the respective columns are sequentially output from a terminal 16. Sums of signal voltages and reset voltages of the respective columns are sequentially output from a terminal 17. When the difference between two outputs is calculated by a subtracting means connected to the output side, a signal voltage containing no reset voltage that varies between pixels can be obtained. Hence, an output with a high S/N ratio, which contains no noise component due to a variation in reset voltage, can be obtained.
As in the first example of prior art, the operation for the first line in the period from time T903 to time T903B is sequentially performed for lines from the second lines even after time T903B, and signals of the respective lines are sequentially output from the terminals 16 and 17.
The scheme of the second example of prior art is called a high-speed shutter scheme.
In the first example of prior art, when an object moves at a high speed, the contents at the upper portion of an image shift from those at the lower portion of the screen, resulting in a distortion in image. If an object is to be photographed by irradiating the object with electronic flash light, the brightness of the object changes between the upper portion of the screen and the lower portion of the screen.
The second example of prior art solves the two problems of the first example of prior art by using charges stored in the photodiodes 101 from time 901 to time 902 as signals of all pixels. However, the second example of prior art has the following problem.
FIG. 6 is a sectional view of each pixel. Referring to FIG. 6, the pixel is formed from the photodiode 101 shown in FIG. 4, floating diffusion region 102 shown in FIG. 4, transfer transistor 103 shown in FIG. 4, a well 130, and a shielding plate 131. Light hxcexd is incident on the pixel. The light incident on the pixel contains obliquely incoming components that reach portions near the floating diffusion region 102 of the photodiode 101 or floating diffusion region 102. Some of charges generated by the light incident on portions near the floating diffusion region 102 of the photodiode 101 make a detour through the transfer transistor 103 and moves to the floating diffusion region 102. Charges are also generated by light incident on the floating diffusion region 102. Even after the charges are transferred from the photodiode 101 to the floating diffusion region 102 at time 903, the number of charges in the floating diffusion region 102 increases as the time elapses. Hence, in the second example of prior art in which charges stored in the floating diffusion region 102 are read out in one frame period sequentially from pixels of the upper line to pixels of the lower line, a noise signal due to the above reason becomes large toward the lower line, and smearing occurs in the output image signal.
It is an object of the present invention to provide a solid-state image pickup element which can prevent any shift between contents at the upper portion of an image and those at the lower portion of the screen even when the object moves at a high speed.
It is another object of the present invention to provide a solid-state image pickup element which can prevent brightness at the upper portion of a screen from changing from that at the lower portion of the screen even in photographing using an electronic flash.
It is still another object of the present invention to provide a solid-state image pickup element which outputs a signal without any smearing due to a variation in charges in a floating diffusion region after transfer of charges from a photoelectric conversion means such as a photodiode.
It is still another object of the present invention to provide a solid-state image pickup element capable of obtaining the image signal of an object by only receiving electronic flash light.
It is still another object of the present invention to obtain an image signal almost free from noise.
In order to achieve the above objects, according to the first aspect of the present invention, there is provided a solid-state image pickup element comprising a plurality of pixel cells each including photoelectric conversion means for photoelectrically converting received light to generate charges, first transfer means for transferring the charges generated by the photoelectric conversion means, first storage means for storing the transferred charges, first output means for time-divisionally outputting a potential generated in the first storage means, and initialization means for initializing the voltage in the first storage means to a predetermined value, means for simultaneously operating the first transfer means of the plurality of pixel cells; means for simultaneously operating the initialization means of the plurality of pixel cells, a plurality of first output lines for receiving outputs from the pixel cells in units of columns, a plurality of second storage means arranged in a one-to-one correspondence with significant pixel cells of the plurality of pixel cells, a plurality of second transfer means for selectively transferring signals of the plurality of first output lines to the plurality of second storage means in units of columns, and control means for controlling the first transfer means, the output means, and the plurality of second transfer means.
According to another aspect of the present invention, there is provided a solid-state image pickup element comprising a sensor unit including a plurality of lines of photoelectric conversion means for generating charges from received light by photoelectric conversion, a memory unit including a plurality of lines of storage means for storing signals from the plurality of lines of photoelectric conversion means, transfer means for transferring a signal from the sensor unit to the memory unit, control means for causing storage means of an arbitrary block in the memory unit to output an image signal from the photoelectric conversion means and causing the photoelectric conversion means corresponding to the storage means of the arbitrary block to output a noise signal, and removal means for removing the noise signal from the image signal.
According to still another aspect of the present invention, there is provided a solid-state image pickup element comprising photoelectric conversion means for generating charges from received light, storage means for storing a signal from the photoelectric conversion means, read means for reading out a first signal output from the photoelectric conversion means and a second signal output from the same photoelectric conversion means through the same storage means, and subtracting means for calculating a difference between the first signal and the second signal, which are read out by the read means.
According to still another aspect of the present invention, there is provided an image pickup apparatus comprising a sensor unit including a plurality of lines of photoelectric conversion means for generating charges from received light by photoelectric conversion, a memory unit including a plurality of lines of storage means for storing signals from the plurality of lines of photoelectric conversion means, transfer means for transferring a signal from the sensor unit to the memory unit, control means for causing storage means of an arbitrary block in the memory unit to output an image signal from the photoelectric conversion means and causing the photoelectric conversion means corresponding to the storage means of the arbitrary block to output a noise signal, subtracting means for calculating a difference between the image signal and the noise signal, and adjustment means for performing at least one of exposure adjustment, focusing adjustment, and zoom adjustment on the basis of a signal output from the subtracting means.
According to still another aspect of the present invention, there is provided an image pickup apparatus comprising photoelectric conversion means for generating charges from received light, storage means for storing a signal from the photoelectric conversion means, read means for reading out a first signal output from the photoelectric conversion means and a second signal output from the same photoelectric conversion means through the same storage means, subtracting means for calculating a difference between the first signal and the second signal, which are read out by the read means, and adjustment means for performing at least one of exposure adjustment, focusing adjustment, and zoom adjustment on the basis of a signal output from the subtracting means.
Other objects, features, and advantages of the present invention will be apparent from the following detailed description in conjunction with the accompanying drawings.